What does that have to do with Dell? They provide a psu that powers the components that came with the computer, they are not going to give you a 1000w psu for future upgrades, I mean cmon get real.
Yeah, I would cancel that order and get yourself something that is much better.
BTW, it isn't Dell's fault. I have numerous Dells at home, one that is running SLI GTX260s w/ stock power supply. It is the decision to purchase that computer, that was designed to run what was purchased with it, that you should be questioning. Not the manufacturer.
I'm sure it will run, but it won't offer the sort of acceleration a true workstation card offers; that's why they are so much more expensive. You'll just have to try it and see how it does.